Post-testicular changes in surface characteristics of the sperm membrane are an intrinsic part of sperm maturation and may be important for sperm function. We propose to analyze in detail changes in externally oriented components of the chimpanzee sperm surface during epididymal transit, at ejaculation and in genital tract fluids and to correlate these with sperm motility and viability. The specific experiments are designed to: 1. characterize, in surface charge, electrophoretic and lectin binding studies, the plasma membrane of chimpanzee sperm during epididymal transit and at ejaculation; 2. analyze biochemically the microenvironment surrounding the sperm during epididymal maturation and at ejaculation and identify those components in the microenvironment which interact specifically with the sperm surface; and 3. correlate effects of male and female genital tract fluids on sperm motility and/or viability with modifications of the sperm surface detected by changes in surfaces charge and in externally oriented protein/glycoproteins accessible to lactoperoxidase-catalyzed iodination. These studies will provide information important for understanding the role of the sperm surface in fertiliazation. In addition, they provide an approach to the development of methods for modifying sperm fertility by manipulating the surface characteristics of epididymal/ejaculated sperm or by altering the micro-environment within the male/female genital tract.